Benedict Cumberbatch
Benedict CumberbatchReuters

There has been no official confirmation on when "Sherlock" season four would air, but buzz on what to expect in the upcoming season has been doing the rounds for a while, with several spoilers hinting the return of Moriarty, and the inclusion of the third Holmes brother.

BBC network has announced a tentative 2016 air date for "Sherlock" season four, before which a one-off Christmas special will be aired.

Meanwhile, fans are excited to know what Moriarty is up to. "Sherlock" actor Benedict Cumberbatch, who has been playing the detective for three seasons, told MTV at the 2014 Comic-Con that he knew what Moriarty's reappearance is all about.

"I casually choose to forget in order to rediscover it again a little bit," said Cumberbatch. "I like casually forgetting, not least because there's a lot of other traffic between then and now but also because it's more fun because it's slightly more fresh. It's a very good idea, I do remember that detail. I'm just trying not to remember it so I don't blurt it out."

Moriarty's reappearance raises a lot of interesting questions. Is he alive and faked his own death, or is he really dead and hatched a plan to kill Holmes before he shot himself in the face and died?

"I can't really say what we're doing with that, but there is no last-minute whim in this," showrunner Steven Moffat told Vulture early this year. "We've had what we're going to do with Moriarty in place from before the second season. Exactly what we're going to do. I remember talking it through with Andrew Scott, who plays Moriarty. Wait and see what's going to happen."

Speculations are also rife that the third Holmes brother will make an appearance in season four and the role is believed to be essayed by an A-list actor. Although no names have been confirmed yet, Tom Hiddleston is a favourite.

The existence of a third brother was hinted in Sherlock's Season three finale, "His Last Vow," when Mycroft tells Sherlock: "I'm not given to outbursts of brotherly compassion. You know what happened to the other one."

On what to expect in the upcoming season, showrunners Moffat and Mark Gatiss said that the fourth instalment will be even more interesting that the preceding seasons, and want fans to be prepared for the unexpected.

"We have a plan to top season 3, and our plan is so devastating that our cast was reduced to tears. (Co-creator) Mark (Gatiss) and I are excited about what we have coming up. We're a couple of fanboys," the writer said, according to Christian Post.

On the track of the storyline, Gatiss added: "We always start with a re-introduction that builds toward a darker climax - we might just be going darker. We've got a very, very good set of ideas," reported Christian Post.

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